1. Field of the Invention
The present invention relates to a liquid crystal display and, more particularly, to a liquid crystal display capable of minimizing noise by preventing deformation of a common electrode made of a metal material and an external electrode of a lamp.
2. Description of the Related Art
In general, currently, the applications for a liquid crystal display (LCD) are growing due to its characteristics that it is lighter, thinner, and driven at a low power consumption. Thus, the LCD is being commonly applied to mobile computers such as notebook computer, office automation equipment, audio/video equipment, or the like.
The LCD displays a desired image on its screen by controlling the amount of transmission of light according to a video signal applied to a plurality of control switch elements arranged in a matrix form.
The LCD includes a liquid crystal panel including a color filter substrate, an upper substrate, and a thin film transistor (TFT) substrate, a lower substrate, and a liquid crystal layer filled therebetween, and a driver that supplies a scan signal and image information to the liquid crystal panel to operate the liquid crystal panel
Compared with a CRT (Cathode Ray Tube) or an LED (Light Emitting Diode), the LCD is not a self-emissive display device and thus does not emit by itself, so it requires a backlight assembly for providing light to the liquid crystal panel.
Light sources for generating light in the backlight assembly include a CCFL (Cold Cathode Fluorescent lamp), an EEFL (External Electrode Fluorescent Lamp), the LED, or the like.
In general, the CCFL has been commonly used as a light source of the LCD, but the use of the CCFL has many problems. First, because an inverter needs to be connected to each CCFL in a one-to-one manner, there is a limitation in reducing the size of the LCD and making the LCD thinner. Second, the fabrication costs increase. Third, the luminance of each lamp varies according to an output voltage and frequency of a transformer installed at an output terminal of each inverter, so the luminance of a displayed screen image is not uniform.
Thus, recently, the EEFL is increasingly employed as the light source for the LCD, and research for the EEFL is actively ongoing.
The EEFL has such a structure that an electric field is formed in a glass tube via an external electrode formed on an external wall surface of both ends of the lamp to discharge a gas within the lamp. Compared with the CCFL, the EEFL can have a relatively long life span and obtain the uniform luminance because a plurality of external electrode fluorescent lamps can be connected in parallel through a single inverter.
The structure of the general LCD having the EEFL as a light source will now be described with reference to FIGS. 1 to 4b. 
With reference to FIG. 1, the general LCD includes a liquid crystal panel 1 for displaying an image, a backlight assembly that supplies light to the liquid crystal panel 1, and an upper cover 7 and a lower cover 8 for receiving and fixing the liquid crystal panel 1 and the backlight assembly therein.
The backlight assembly includes lamps 2 that emit light, an optical sheet 9 positioned at an upper potion of the lamps 2 to increase light efficiency, first support sides 4 positioned at upper portions of both ends of the lamps 2, and second support sides 5 positioned at lower portions of both ends of the lamps 2.
Each lamp 2 includes a glass tube 2a in which phosphor is coated on an inner wall to emit light, and an external electrode 2b provided at both ends of the glass tube 2a. 
In the general LCD, common electrodes 3 are mounted on the second support sides 5 to supply power to the external electrodes 2b of the lamps 2. The common electrodes 3 includes an electrode holder 3a contacting with the external electrodes 2b of the lamps 2 in a surrounding manner to fix the lamps 2 and supplying power to the lamps 2 and common units 3b having a two-bar shape and connected with both ends of the electrode holders 3a. Power supplied to the common electrodes 3 from the exterior is applied to the external electrodes 2b of the lamps 2 through the electrode holders 3a to form an electric field in the lamps 2, to thus allow the lamps 2 to emit light.
As shown in FIG. 2, a plurality of common electrode supports 4a are provided on the first support sides 4. The plurality of common electrode supports 4a extend from an inner surface to come in contact with the common electrodes 3 to support and fix the common electrodes 3. The common electrode supports 4a are formed such that they have a width similar to the width of the lamps 2 of the first support sides 4 in a lengthwise direction so as to be in contact with the common units 3b having the two-bar shape at one time.
With reference to FIG. 3, the general LCD having such a configuration as described above has the following problem. Because the common electrode supports 4a serve as barriers barring between the lamps 2, heat generated from the lamps 2 is not circulated but kept in the narrow space, the temperature in the first and second support sides 4 and 5 goes up sharply when driven. Then, the common electrodes 3 made of a metal material and the external electrodes 2b of the lamps 3 expand according to the temperature increase, to frictionally contact with the first and second support sides 5 and 5 made of a plastic material to generate noise.
In addition, after the LCD is driven for a certain time period, when power is cut off, the common electrodes 3 and the external electrodes 2b of the lamps 2, which have been expanded by heat during the driving operation, are contracted to frictionally contact with the first and second support sides 4 and 5 to generate noise.
The problem will now be described in detail with reference to FIGS. 4a and 4b. 
FIG. 4a is a graph showing changes in the strength of noise according to the lapse of time based on a driving start time of the related art LCD as a reference, and FIG. 4b is a graph showing changes in the strength of noise according to the lapse of time based on a power cutoff time of the related art LCD as a reference after the LCD is driven for a certain time period.
With reference to FIG. 4a, when the related art LCD was operated (or driven), the detected noise level has a maximum value of about 39.5 [dB], which is a value that was measured at 481 seconds after the start of operation. Also, referring to FIG. 4b, when the power of the related art LCD was cut off after the LCD operated for a certain duration, the detected noise level has a maximum value of about 34.5 [dB], which is a value that was measured at 133 seconds after power cut off.
Thus, because the related art LCD generates the noise 39.5 [dB] and 34.5 [dB], which are sufficient to make the user uncomfortable, the user would feel stressed in using the related art LCD.